High Modulus Reinforcement Alloys

Materials used as reinforcement for conductors in high-field magnets require both a high capacity for load bearing and a high resistance to deformation under stress; that is, a high value for tensile strength and a high modulus of elasticity. In addition, compatibility between the magnet conductor and any proposed reinforcement materials and has to be carefully evaluated in terms of their capability for thermal expansion, stability at high temperature, resistance to oxidation, and crack propagation. We investigated a number of (nickel based and nickel-cobalt based) superalloys designed for high-temperature applications. These superalloys have higher Young's modulus than the stainless steels that are currently used as reinforcement materials for high-field magnets. Our test materials were subjected to thermo-mechanical processing that strengthens the alloys by forming very fine particles within them. Our initial work focused on changes that occured in the alloy during deformation at either cryogenic or room temperature. Because we observed distinct interfaces between the particles and the matrix, we decided that these materials could be described as precipitate-strengthened alloys. Both the strengthening component area and the matrix had more resistance to plastic deformation at cryogenic temperatures, than at room temperatures. In some cases, we further enhanced the strength of the alloy by doping them with other elements. In all the cases, these alloys permitted more efficient performance of conductors by shareing more of the load than would be possible with stainless steel reinforcement materials. This paper outlines the properties of these new alloys and establishes their compatibility with certain conductors commonly used for high-field magnets.